Ultrasonic diagnostic techniques such as compound B-scans and Doppler motion detection are now widely used in clinical medicine and the extent, the fields of use and the methods of ultrasound application are rapidly increasing. Thus significantly large and increasing numbers of population are exposed to ultrasonic radiation of various frequencies, intensity levels and dosage schedules. The developing fetus in particular is often subjected to a whole body irradiation during the ultrasonic examination of the mother. Although no injuries or abnormalities attributable to diagnostic ultrasonic procedures have so far been reported, conflicting data on the production of chromosomal abnormalities in cells in suspension have recently been published. Retardation of the rate of growth in chick embryos irradiated with diagnostic pulsed ultrasound has also been reported, as have mutagenic effects in plant cells, bacteria and insects though no such effects were found in mice. These conflicting and mostly sketchy reports under-line the need for critical and definite studies to establish the safety of ultrasonic procedures. Apriori, rapidly proliferating cells, whether in the fetus or in the adult, would be expected to be more susceptible to injury than the stable, mature cells. The research proposed in this application aims to establish the toxic levels of ultrasonic energy which interfere with cell replication and its relation to diagnostic levels. It also seeks to determine whether sub-lethal damage is produced and if there is variation in radiation sensitivity within the cell cycle. Dose-response curves for clonal survival obtained with asynchronous monolayer cultures, will provide a scaling factor for measuring the toxic levels of ultrasonic energy as compared with diagnostic levels. Split-dose technique will be utilized to determine the occurrence of sub-lethal damage and repair. The relative sensitivity of the cells in the various stages of the cell cycle will be determined by using synchronized cultures.